Apparatus and devices of the type with which the invention is concerned are described in U.S. Pat. No. 5,271,297 and in U.S. patent application Ser. No. 08/005,560 filed Jan. 19th, 1993 in the name Siegfried Heiermann both assigned to the same assignee as this application. A tensioning or clamping apparatus is also described in GB 1444606 in which piston and cylinder units supported on a carrier ring subject couplings on the screw-threaded members to tensile force. In this arrangement, each of the couplings and the heads of the screw-threaded members have inter-engageable jaws and grooves. The nuts on the screw-threaded members lie beneath the couplings relative to the vessel and are rotated with a special drive having a pinion wheel which can pass through apertures in the carrier ring to mesh with teeth on the nuts. When one of the nuts is connected to the drive and is to be rotated an associated piston and cylinder unit is charged with pressure fluid to lift the coupling and brace the screw-threaded member so the nut can be rotated on the screw-threaded member.
U.S. Pat. No. 3,844,533 also describes a tensioning or clamping device which is moved from one member to the next to perform its function.
The known apparatuses and devices cannot ensure that all the screw-threaded members are subjected to the same tensioning forces since the individual screw-threaded members often require tensioning forces of different values. It is above all desirable to tighten the nuts on the cover to a uniform extent to provide a good seal.
It is a general object of the invention to provide an improved apparatus and device which can ensure more uniform tensioning of the screw-threaded members.